1. Field of the Invention
The present invention relates to a display device. More particularly, the present invention relates to a display device such as a liquid-crystal display device, a plasma display panel (hereinafter abbreviated as xe2x80x9cPDPxe2x80x9d), or an electroluminescent display (hereinafter abbreviated as xe2x80x9cELxe2x80x9d) device, and to an image signal processing method which is applicable to these display devices.
2. Description of the Related Art
Recently, display devices, such as liquid-crystal displays (hereinafter abbreviated as xe2x80x9cLCDsxe2x80x9d), have been used in various fields. Generally, an LCD for color display has contained therein a 6-bit or 8-bit digital driver for each of the colors of R (red), G (green), and B (blue). For example, according to an LCD having an 8-bit digital driver, a display of 256 gradations for each color is possible, and a display of 16.7 million gradations is possible as a whole. However, even though an LCD of such a degree has a sufficient performance as a consumer-oriented general-purpose monitor, such as a mere OA (Office Automation) apparatus, it has an insufficient performance as an industrial monitor for medical and broadcast purposes, and there has been a demand for a further increase in the number of gradations.
For example, in a case where 8-bit image data for use in a video signal is input to a conventional LCD having only a 6-bit digital driver, that is, in a case where the number of displayable gradation bits of a display device is smaller than the number of gradation bits which represent the image data which is input to the display device, a method is employed in which the number of gradations of the display device is increased in a pseudo-manner by causing components, which cannot be displayed, within the image data in a single arbitrary pixel (in this case, two low-order bits), to diffuse into adjacent pixels in the periphery of the same screen frame (intra-frame error diffusion). Furthermore, a technique, which is what is commonly called frame rate control (hereinafter abbreviated as xe2x80x9cFRCxe2x80x9d), is also employed in which an arbitrary pixel is caused to flash in intervals of temporally continuous frames.
In recent years, the number of displayable gradation bits of a display device has been increased, and an LCD included with a personal computer or the like comes standard with an installed 8-bit digital driver. Therefore, if 8-bit image data is input to an LCD having an 8-bit digital driver, a display can be produced without using the above-mentioned pseudo-gradation processing technique. However, in the manner described above, for medical and broadcast applications, there are cases in which the original image data before being input to a personal computer is 10 bits long. In such a case, even if an LCD capable of displaying only gradation levels for 8 bits, there is a demand for producing the equivalent of a 10-bit display in a pseudo-manner.
A case is assumed in which, in an LCD of an XGA (Extended Graphics Array) method in which the number of pixels of one scanning line is 1024, image data with a ramp waveform is displayed on one scanning line. In the case of a ramp waveform, for 8-bit image data representing 256 gradation levels, the gradation level is 0 at one end of the scanning line, the gradation level increases by one at intervals of 4 pixels from the one end toward the other end, and the gradation level is 255 at the other end. When this type of display is produced, problems seldom occur in consumer-oriented applications, but even if the gradation level changes by one, which is the finest resolution of this LCD, this is still large in terms of the degree of the gradation change, and even in the case of image data with a ramp waveform in which the luminance change should be the most moderate, there is a case in which the boundary between images is visually recognized.
Generally, in order that the number of gradation bits be increased in a pseudo-manner when the number of gradation bits of a display device is equal to the number of gradation bits of image data, the above-mentioned pseudo-gradation processing technique, such as intra-frame error diffusion or FRC, may be used. However, these techniques simply generate intermediate gradation levels in a pseudo-manner by mechanically computing the low-order bits of image data, and do not meet the demand for a more moderate gradation change.
The present invention has been made to solve the above-described problems. It is an object of the present invention to provide a display device and an image signal processing method, which generate intermediate gradation levels in a pseudo-manner and which realize an image display having a more natural luminance change without undergoing the limitation of the number of gradation bits of input image data.
To achieve the above-mentioned object, according to one aspect of the present invention, there is provided a display device comprising gradation change detection means for generating a control signal when a gradation change of one gradation level is detected between adjacent image data among a plurality of pieces of image data which is input continuously with respect to time, and when it is detected that the numbers of gradations of a plurality of pieces of image data input before this gradation change are equal to each other and the numbers of gradations of a plurality of pieces of image data input after this gradation change are equal to each other, in a case where one screen is displayed on a display section according to a plurality of fields or frames, and when the number of gradation bits possessed by image data is equal to the number of gradation bits possessed by the display section, a display of a number of gradation bits, which is greater than these numbers of gradation bits, is produced by the display section; and image data conversion means for receiving the control signal and performing at least one of (i) the process for converting the gradation level of image data before the gradation change into the gradation level of image data after the gradation change either in one of two fields which are adjacent with respect to time or in one of two frames which are adjacent with respect to time, and (ii) the process for converting the gradation level of image data after the gradation change into the gradation level of image data before the gradation change either in one of two fields which are adjacent with respect to time or in one of two frames which are adjacent with respect to time.
Here, the xe2x80x9cnumber of gradation bitsxe2x80x9d refers to the number of bits, such as 6 (bits) or 8 (bits), which represents the gradation of a display section and image data, as described in the xe2x80x9cDescription of the Related Artxe2x80x9d. Furthermore, the xe2x80x9cgradation levelxe2x80x9d refers to a data sequence, which is 6 bits or 8 bits long, representing gradations, for example, xe2x80x9c11111111xe2x80x9d for 8 bits (255 gradation levels in decimal).
In the display device of the present invention, the gradation change detection means detects that there is a gradation change of one gradation level between adjacent image data among a plurality of pieces of image data which is input continuously with respect to time, and that the numbers of gradations of a plurality of pieces of image data input before this gradation change are equal to each other and the numbers of gradations of a plurality of pieces of image data input after this gradation change are equal to each other, and generates a control signal at this time. The description xe2x80x9cthere is a gradation change of one gradation level between adjacent image data among a plurality of pieces of image data which is input continuously with respect to time, and that the numbers of gradations of a plurality of pieces of image data input before this gradation change are equal to each other and the numbers of gradations of a plurality of pieces of image data input after this gradation change are equal to each otherxe2x80x9d refers to, for example, image data representing a portion with a ramp waveform, described in the section xe2x80x9cDescription of the Related Artxe2x80x9d and refers to a case in which gradation changes are the most moderate.
Then, the image data conversion means receives the control signal which is output from the gradation change detection means, and performs at least one of (i) the process for converting the gradation level of image data before the gradation change into the gradation level of image data after the gradation change either in one of two fields which are adjacent with respect to time or in one of two frames which are adjacent with respect to time, and (ii) the process for converting the gradation level of image data after the gradation change into the gradation level of image data before the gradation change either in one of two fields which are adjacent with respect to time or in one of two frames which are adjacent with respect to time. That is, by changing the gradation level of image data before a gradation change into the gradation level after the gradation change or by changing the gradation level of image data after a gradation change into the gradation level before the gradation change between adjacent fields or frames, the location of the gradation change is shifted by one piece of data between adjacent fields or frames. Then, to the human eye, the image data of the location where the gradation level is changed is visually recognized as an intermediate gradation level of one or less gradation level. In this manner, gradation levels are created in a pseudo-manner, and an image display having a more natural luminance change can be realized.
In the image data conversion means, preferably, at least one of the process for converting the gradation level of one or two pieces of image data before the gradation conversion and the process for converting the gradation level of one or two pieces of image data after the gradation conversion is performed.
The reason for this is that, for example, if 3 or more pieces of image data are to be converted, the processing circuit becomes complex, and the circuit scale becomes large sharply.
In a case where a control signal is generated from the gradation change detection means with respect to each piece of the image data of two pixels positioned in the same column of two adjacent rows within a display section, preferably, the image data conversion means makes a change as to the conversion of the gradation level of image data before the gradation change and the conversion of the gradation level of image data after the gradation change between the image data of the two pixels.
The reason for this is that, if the timings at which the numbers of gradations are converted are aligned for the pixels arranged in a column (vertical) direction among a plurality of rows (scanning lines) which form the screen either before the gradation change or after the gradation change, an undesirable case may occur in which a flicker is seen in the vertical direction. Therefore, in such a case, for upper and lower pixels, if the gradation level of one part is converted before a gradation change and the gradation level of the other part is converted after a gradation change, the problem of a flicker being seen in the vertical direction is solved.
In a similar manner, when a control signal is generated from the gradation change detection means with respect to each piece of the image data of the two pixels positioned in the same row of two adjacent columns within the display section, preferably, the image data conversion means makes a change as to the conversion of the gradation level of image data before a gradation change between the image data of the two pixels or the conversion of the gradation level of image data after a gradation change.
With this construction, the problem of a flicker being seen in the horizontal direction is solved.
According to another aspect of the present invention, there is provided a image signal processing method comprising the step of: performing at least one of (i) the process for converting the gradation level of image data before a gradation change into the gradation level of image data after a gradation change either in one of two fields which are adjacent with respect to time or in one of two frames which are adjacent with respect to time, and (ii) the process for converting the gradation level of image data after a gradation change into the gradation level of image data before a gradation change either in one of two fields which are adjacent with respect to time or in one of two frames which are adjacent with respect to time, based on a detection result when it is detected that there is a change of one gradation level between adjacent image data among a plurality of pieces of image data which is input continuously with respect to time, and that the numbers of gradations of a plurality of pieces of image data input before this gradation change are equal to each other and the numbers of gradations of a plurality of pieces of image data input after this gradation change are equal to each other, in a case where, when the number of gradation bits possessed by image data is equal to the number of gradation bits possessed by a receiving side which receives the image data, a process for receiving a number of gradation bits, which is greater than these numbers of gradation bits, is performed by the receiving side.
In the image signal processing method of the present invention, first, it is detected that there is a gradation change of one gradation level between adjacent image data among a plurality of pieces of image data which is input continuously with respect to time, and that the numbers of gradations of a plurality of pieces of image data input before this gradation change are equal to each other and the numbers of gradations of a plurality of pieces of image data input after this gradation change are equal to each other. The description xe2x80x9cthere is a gradation change of one gradation level between adjacent image data, and the numbers of gradations of a plurality of pieces of image data input before this gradation change are equal to each other and the numbers of gradations of a plurality of pieces of image data input after this gradation change are equal to each otherxe2x80x9d refers to image data representing a portion with a ramp waveform, described, for example, in the section xe2x80x9cDescription of the Related Artxe2x80x9d, and refers to a case in which gradation changes are the most moderate.
Then, based on this detection result, at least one of (i) the process for converting the gradation level of image data before the gradation change into the gradation level of image data after the gradation change either in one of two fields which are adjacent with respect to time or in one of two frames which are adjacent with respect to time, and (ii) the process for converting the gradation level of image data after the gradation change into the gradation level of image data before the gradation change either in one of two fields which are adjacent with respect to time or in one of two frames which are adjacent with respect to time is performed.
That is, by changing the gradation level of image data before a gradation change into the gradation level after a gradation change or by changing the gradation level of image data after a gradation change into the gradation level before a gradation change between adjacent fields or frames, the location of the gradation change is shifted by one piece of data between adjacent fields or frames. Then, to the human eye, the image data of the location where the gradation level is changed is visually recognized as an intermediate gradation level of one or less gradation level. In this manner, intermediate gradation levels are created in a pseudo-manner, and an image display having a more natural luminance change can be realized.
When an image data conversion process is performed, preferably, at least one of the process for converting the gradation level of one or two pieces of image data before the gradation conversion and the process for converting the gradation level of one or two pieces of image data after the gradation conversion is performed.
The reason for this is that, for example, if 3 or more pieces of image data are to be converted, the processing method becomes complex, and the circuit scale becomes large sharply.
In a case where a control signal is generated with respect to each piece of the image data of two pixels positioned in the same column of two adjacent rows on a receiving side, a change is made as to the conversion of the gradation level of image data before the gradation change and the conversion of the gradation level of image data after the gradation change between the image data of the two pixels.
The reason for this is that, if the timings at which the numbers of gradations are converted are aligned for the pixels arranged in a column (vertical) direction among a plurality of rows (scanning lines) which form the screen either before the gradation change or after the gradation change, an undesirable case may occur in which a flicker is seen in the vertical direction. Therefore, in such a case, for upper and lower pixels, if the gradation level of one part is converted before a gradation change and the gradation level of the other part is converted after a gradation change, the problem of a flicker being seen in the vertical direction is solved.
In a similar manner, with respect to each piece of the image data of the two pixels positioned in the same row of two adjacent columns on the receiving side, preferably, a change is made as to the conversion of the gradation level of image data before a gradation change between the image data of the two pixels or the conversion of the gradation level of image data after a gradation change.
According to this method, the problem of a flicker being seen in the horizontal direction is solved.
The above and further objects, aspects and novel features of the invention will become more fully apparent from the following detailed description when read in conjunction with the accompanying drawings.